How to identify Malachite on Limonite/Goethite

To correctly identify Malachite on Limonite/Goethite (Cu2(CO3)(OH)2 (Malachite) on FeO(OH) (Limonite/Goethite)), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.

Step-by-step identification

1. 1

   Color

   Overall color and any zoning or banding

   Malachite is typically bright green to dark green, often with concentric banding. Limonite/Goethite is yellowish-brown, reddish-brown, or dark brown.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Malachite can be silky (fibrous varieties), vitreous (crystalline), or dull (earthy). Limonite/Goethite is typically dull, earthy, or submetallic.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Malachite often forms botryoidal, mammillary, stalactitic, or radiating fibrous aggregates. Limonite/Goethite is typically earthy, porous, massive, or botryoidal.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Malachite: Monoclinic, often acicular, fibrous, or tabular crystals, but more commonly massive, botryoidal, or stalactitic. Limonite/Goethite: Orthorhombic (Goethite), but typically cryptocrystalline or amorphous in massive forms (Limonite).

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Malachite: Perfect on {001}, good on {201}. Limonite/Goethite: No distinct cleavage, but Goethite has perfect cleavage on {010}.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Supergene enrichment zones of copper sulfide deposits, often found in gossans (iron-rich weathered caps of ore bodies).

Key Facts

Hardness

Malachite: 3.5-4 on Mohs scale. Limonite/Goethite: 5-5.5 (Goethite), variable (Limonite).

Specific Gravity

Malachite: 3.9-4.03. Limonite/Goethite: 3.3-4.3 (Goethite), variable (Limonite).

Crystal System

Malachite: Monoclinic. Limonite/Goethite: Orthorhombic (Goethite), amorphous/cryptocrystalline (Limonite).

Color

Malachite: Bright green to dark green. Limonite/Goethite: Yellowish-brown, reddish-brown, dark brown.

Luster

Malachite: Silky, vitreous, dull. Limonite/Goethite: Dull, earthy, submetallic.

Transparency

Malachite: Translucent to opaque. Limonite/Goethite: Opaque.

Fracture

Malachite: Uneven to subconchoidal. Limonite/Goethite: Uneven, splintery, conchoidal.

Cleavage

Malachite: Perfect on {001}, good on {201}. Limonite/Goethite: No distinct cleavage (Limonite), perfect on {010} (Goethite).

Composition

Malachite: Hydrous copper carbonate. Limonite/Goethite: Hydrous iron oxide.

Physical characteristics

• Crystal Habit: Malachite: Botryoidal, mammillary, stalactitic, fibrous, massive, rarely distinct crystals. Limonite/Goethite: Massive, earthy, botryoidal, stalactitic, reniform.
• Cleavage Type: Malachite: Perfect in one direction, good in another. Limonite/Goethite: None observed in massive forms, perfect in one direction for Goethite.
• Fracture Type: Malachite: Uneven to subconchoidal. Limonite/Goethite: Uneven, splintery, conchoidal.
• Tenacity: Malachite: Brittle. Limonite/Goethite: Brittle to friable.
• Luster Type: Malachite: Silky, vitreous, dull. Limonite/Goethite: Dull, earthy, submetallic.

Explore Malachite on Limonite/Goethite